1. Field of the Invention
The present invention relates to a method for manufacturing a condenser microphone and more particularly, to a method for manufacturing a condenser microphone capable of directly bonding a field effect transistor (hereinafter, referred to as FET) chip which is formed on a wafer on a printed circuit board, thereby achieving miniaturization of the condenser microphone and improving the product characteristic.
2. Description of the Related Art
Generally, a condenser microphone is comprised of a condenser where a thin conductive film of diaphragm and a fixed electrode are arranged in parallel, for converting the vibration of sound into an electrical signal to obtain an electrical output.
The condenser microphone is used in a mike, a telephone or a tape record.
FIG. 1 is a separated perspective view illustrating the construction of a conventional condenser microphone, and FIG. 2 is a sectional view taken along a predetermined portion of FIG. 1.
As shown, the conventional condenser microphone includes: a case 8 through which a sound wave inflow hole 9 is formed; a filter 11 positioned on the top portion of the case 8, for preventing dust, moisture and foreign materials from flowing into the case 8 through the sound wave inflow hole 9; a diaphragm ring 7 positioned on the interior of the case 8, for maintaining a space in the interior of the case 8 to induce the vibration of sound flowing through the sound wave inflow hole 9; a diaphragm 6 positioned on the bottom end of the diaphragm ring 7 and vibrated by the sound flowing through the sound wave inflow hole 9; a spacer 5 positioned on the bottom end of the diaphragm 6, for maintaining the vibration state of the diaphragm 6 to transmit the vibration of sound; a supporter 3 positioned on the bottom end of the spacer 5, for supporting each part to prevent the movement thereof and the change of the whole shape of the condenser microphone; a back-pole plate 4 positioned on the interior of the supporter 3, for maintaining the vibration state, while being separated by a predetermined interval from the diaphragm 6 by means of the spacer 5 and for detecting capacitance which is varied in accordance with an amount of vibration of the diaphragm 6; a connection ring 10 positioned in the interior of the supporter 3 and on the bottom end of the back-pole plate 4, for connecting the gate of an FET 2 and the back-pole plate 4; a printed circuit board 1 on which a circuit of a conductive material is wired; and the FET 2 bonded on the printed circuit board 1, for amplifying and converting potential variation according to the variation of the capacitance into an electrical signal.
In this case, the FET 2 is packaged and produced by a semiconductor company. The packaging process of the FET 2 is carried out as follows: Firstly, a wafer is scribed in a predetermined size and the FET chip is formed on each of the scribed cells. Then, after cutting each FET chip formed on the wafer, a predetermined length of needle is bonded on the gate, the source and the drain, respectively, formed on the bottom surface of the FET chip. Next, a molding process is carried out for each bonded FET by means of an epoxy resin, thereby producing the FET 2.
In the conventional practice, the condenser microphone is manufactured by using the FET 2 produced by the above-mentioned process.
Referring to FIG. 1 showing the separated perspective view of the condenser microphone manufactured in the conventional practice, the diaphragm ring 7, the vibration 6, the spacer 5, the back-pole plate 4 and the supporter 3 are assembled in the named order into the case 9. Finally, the printed circuit board 1 on which the FET 2 is soldered is fixedly coupled on the bottom end of the supporter 3 and the case 9, thereby manufacturing one condenser microphone.
In this case, the coupling process of the FET 2 with the printed circuit board 1 in the soldering manner is carried out as follows:
Firstly, each of the drain, source and gate terminals of the FET 2 is connected to the corresponding hole provided on the printed circuit board 1, and the gate terminal of the FET 2 is connected to the back-pole plate 4. The connection of the gate terminal of the FET 2 and the back-pole plate 4 is achieved by a point contact method or by using the connection ring 10. Recently, the connection ring connecting method is widely used.
To connect the FET 2 and the printed circuit board 1, the end of each of the drain, source and gain terminals is bent at a predetermined angle toward the printed circuit board 1.
The bent end of each of the drain, source and gain terminals is inserted into a through hole provided on the printed circuit board 1. The drain, source and gain terminals, which are passed through the printed circuit board 1 via the through hole, are protruded on the rear surface of the printed circuit board 1. And, the end of the protruded drain, source and gain terminals is re-bent at a predetermined angle to surround the printed circuit board 1, with a consequence that the FET 2 and the printed circuit board 1 are temporarily fixed. After the manufacturing process, each terminal, which has been bent to fix the FET 2 and the printed circuit board 1, should be bent to its original state.
In this case, the connection of the FET 2 and the printed circuit board 1 is achieved in a soldering manner or by using an SMD (Surface Mount Device).
After the completion of the connection of the FET 2 and the printed circuit board 1, the printed circuit board 1 is assembled in the interior of the case 9, thereby manufacturing the condenser microphone.
The size of the condenser microphone is determined upon the size of the FET 2, and if the condenser microphone is manufactured by using the FET 2 as mentioned above, the thickness `L` of the condenser microphone is ranged up to 1.5 (mm).
However, the conventional condenser microphone arises the following some problems that since the drain, source and gate terminals are repeatedly bent, the bent portions may be disconnected; that since the terminals of the FET 2 and the printed circuit board 1 are bonded in the soldering manner, a undesirable noise may be generated due to contact resistance; and that if heat is applied on the rear surface of the printed circuit board 1 for wiring, the terminals connected to the FET 2 may be disconnected.
On the other hand, the conventional method for manufacturing the condenser microphone is dependent upon the production method and amount determined by the semiconductor manufacturing company producing the FET as a main member of the condenser microphone, which will place restrictions on an amount of the production of the condenser microphone.